The artist says that it is an AKM, wich seems to be an improvement over the AK-47. That muzzle corresponds to an AKM but I'm not an expert.

Correct; the stamped receiver and corresponding fire selector lever here also visibly distinguish it as an AKM vs. an AK. (The black polymer furniture comes from the factory on neither, but presumably this is what's "custom" per the artist commentary.)

Per the back-and-forth tag editing, this isn't an AK-74 due to the different gas block and front sight tower (the bayonet lug on an AK-74 is on the front sight tower behind the notch for the cleaning rod, rather than below the gas block.)